U.S. Pat. No. 4,614,569 describes anodes for aluminium electrowinning coated with a protective coating of cerium oxyfluoride, formed in-situ in the cell or pre-applied, this coating being maintained by the addition of cerium to the molten cryolite electrolyte.
U.S. Pat. No. 4,948,676 describes a ceramic/metal composite material for use as an anode for aluminium electrowinning particularly when coated with a protective cerium oxyfluoride based coating, comprising mixed oxides of cerium and one or more of aluminium, nickel, iron and copper in the form of a skeleton of interconnected ceramic oxide grains interwoven with a metallic network of an alloy or an intermetallic compound of cerium and one or more of aluminium, nickel, iron and copper.
U.S. Pat. No. 4,909,842 discloses the production of dense, finely grained composite materials with ceramic and metallic phases by self-propagating high temperature synthesis (SHS) with the application of mechanical pressure during or immediately after the SHS reaction.
U.S. Pat. No. 5,217,583 describes the production of ceramic or ceramic-metal electrodes for electrochemical processes, in particular for aluminium electrowinning, by combustion synthesis of particulate or fibrous reactants with particulate or fibrous fillers and binders. The reactants included aluminium usually with titanium and boron; the binders included copper and aluminium; the fillers included various oxides, nitrides, borides, carbides and silicides. The described composites included copper/aluminium oxide-titanium diboride etc.
PCT patent application No. W092/22682 describes an improvement of the just mentioned production method with specific fillers. The described reactants included an aluminium nickel mixture, and the binder could be a metal mixture including aluminium, nickel and up to 5 weight % copper.
U.S. Pat. Nos. 4,374,050 and 4,374,761 disclose anodes for aluminium electrowinning composed of a family of metal compounds including oxides. It is stated that the anodes could be formed by oxidising a metal alloy substrate of suitable composition. However, it has been found that oxidised alloys do not produce a stable, protective oxide film but corrode during electrolysis with spalling off of the oxide. U.S. Pat. No. 4,620,905 also discloses oxidised alloy anodes.
U.S. Pat. Nos. 4,454,015 and 4,678,760 disclose aluminium production anodes made of a composite material which is an interwoven network of a ceramic and a metal formed by displacement reaction. These ceramic metal composites have not been successful.
U.S. Pat. Nos. 4,960,494 and 4,956,068 disclose aluminium production anodes with an oxidized copper-nickel surface on an alloy substrate with a protective barrier layer. However, full protection of the alloy substrate was difficult to achieve.
U.S. Pat. No. 5,284,562 discloses alloy anodes made by sintering powders of copper, nickel, and iron. However, these sintered alloy anodes cannot resist electrochemical attack.
PCT application No. PCT/US93/03605, filed Oct. 27, 1994 discloses aluminium production anodes comprising ordered aluminide compounds of nickel, iron and titanium produced by micropyretic reaction with a cerium-based colloidal carrier.
So far, all attempts to produce an electrode suitable as anode for aluminium production and based on metals such as nickel, aluminium, iron and copper or other metals have proven to be unsuccessful in particular due to the problem of poor adherence due partly to thermal mismatch between the metals and the oxide formed prior to or during electrolysis.